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Subwoofer Calibration Using Rives Audio Test CD 2

by August 24, 2004

If you bought a sub-woofer lately and had the pleasure or displeasure of trying to integrate it into your existing system, then hopefully this review will be good news to you. The good news is; there is help and it is affordable. The bad news is; you will need to invest in some basic tools, such as the Radio Shack Analog Sound Level Meter , the Rives Audio Test CD 2 and an equalizer to put in line with your sub. The more bands your equalizer has in the bass region the better. Now I am not going to cover all the details on subwoofers and setup because there are already many fine articles on the subject, however, I will mention a couple of things you may or may not already know.

  • First, if your sub is too far out of balance with the rest of your system, then it can really mess everything up. This is most noticeable in the midrange and can really have a detrimental affect on movie dialog.
  • Second, some rooms can't simply be tamed with an equalizer alone and may require room treatment, subwoofer/speaker relocation, listener relocation or all of these. In an ideal setup one would always want to treat the room, optimize speaker and listening position then use an EQ to fine-tune it. However, this is not always affordable or practical to some and they may already have two of the items mentioned to at least achieve better sounding bass than what they may have now. This was the case for me.
  • Third, what we are mostly trying to achieve is to smooth out the peaks in the subs bass response. You should rarely attempt to electronically compensate for any large dips or nulls. If the nulls are just a few db's then a little boost is Ok, and I do stress little. There may also be some peaks that just can't be tamed by your EQ. If that is the case, you will have to treat the room, relocate the speakers/listener or just learn to live with it. Unless your room and/or speaker system has severe issues you, you should be able to make a noticeable improvement in your systems bass response following this basic procedure using the tools outlined herein.

What is the RIVES Audio Test CD ? Well basically it just a CD with a series of tones to help you calibrate and evaluate your system. The tones are 1/3 octave from 20Hz to 20khz. However, it has something no other test CD I know of has. It has a set of tones that are compensated for the response of the Radio Shack analog SPL meter. It also has tests for evaluating phasing, and some very excellent sounding music tracks courtesy of MapleShade, which leads to me to my one of two minor complaints about the CD. I wish the music tracks were complete songs (not partial) and also included some electronic jazz or fusion to further evaluate your bass performance. Since this CD has tones that go all the way up to 20,000 kHz, it can be used to calibrate the entire spectrum if you have the setup to do so. However, since calibrating bass response is the focus of this article, I will limit this discussion accordingly for this review. I ordered my CD direct from their website and it arrived promptly in two days. It also included literature for some of their other products that looked very nice, however, they are little out my budget at this time so I am thankful they thought of guys like me and made this CD. The included instructions are brief but very concise and do a good enough job explaining all the steps. Also they assume you know how to use an EQ so they don't cover that either. I would prefer some more detail and maybe a few FAQ's but that's just a preference not a complaint.

Subwoofer Calibration Procedure

Step 1 : Download and print the chart for plotting room response. It is available for free on their website. ( Chart )

RadioShackSPLmeter.jpg

Step 2: Set the SPL meter on a tripod in your primary listening position. Set the meter response for "Slow C-Weighted" and rotate the dial to the 80db setting. 80 db is a good level to use when evaluating bass response. Be careful when listening to the higher tones at levels above 80db. If your speakers are not up to the task, you could be looking at blown drivers. I have seen it happen. Not with this disk and these tones but be careful nonetheless. Rives mentions this as well.

Step3: Starting with your volume down low, play the 1000Hz tone from the compensated set of tones and raise it until you reach the 0 point on the meter. This will be 80db. It may help to loop the track until you have it correct.

Step 4: Starting with the first compensated tone run through all of them and mark them on your chart. You will now have a graph or your room response with 1/3 octave resolution.

Step 5: Now you will need to determine if your sub is in an adequate location to begin the process of lowering the peaks with the EQ. If your peaks are not too severe (less than +10db compared to the rest of the bass spectrum), run through the tones again and begin adjusting with the EQ to minimize peaks. When you are satisfied repeat step 4 by charting a new graph. If you have some problems with the first pass, then try relocating your subwoofer and start again. I said this was affordable, I never said it would be easy.

After the first pass, it was apparent that I had some serious issues. I had a huge peak (+20db) at the 63Hz point, one at 40Hz and some peaks in the 100-160Hz range. This is something I would have never known without running these test tones.

This meant when I set my subs level with the SPL meter and the pink noise from my receiver, what I was really in effect doing was setting the bass level to the peak at 63Hz and all the other frequencies were being obscured.

sub_precalibration.gif

In reality I was down 21db at 30Hz. That also explains why the gain on my subwoofer was always so low.

Locating the Subwoofer

sub_hockeypucks.jpg

Now I could begin the process of finding a better location for the sub. This is what I did to get a flatter response in my room. There are several schools of thought on this and since every room is different your steps and conclusions will no doubt be different too.

I initially used the crawling for bass technique when I placed my sub, but because of my room I found this was not ideal. I attached long cords on my sub, placed the offending 63Hz tone on repeat and started moving my sub around the room until I got the tone into a more manageable range.

After trying no less than eight places, I settled on the front right corner. Incidentally, I had to turn my front firing sub into a down firing one. Hockey pucks worked great for this and they are only .99 cents each. Also, I had to increase the amount of delay to 20 feet even though the subwoofer is only 13 feet away. I could watch the peak at 63Hz rise and fall as I played with the delay settings. Without using a SPL meter and this CD, I would have never been able to see this either.

Remeasuring the Sub

Now according to the Rives CD and the tones, I was only up 8db at 63 and dead on at 31.5Hz. Now I had good subwoofer positioning to begin tweaking the response with the EQ. Since my sub is only rated flat down to 27Hz, I did not touch any of the EQ settings from 25hz and below and I lowered the bands from 80Hz to 160hz to account for any overlap in the receivers cross over. My final results were pretty respectable from 31 to 160.

sub_aftercalibration.gif

My bass was now almost ruler flat according to the meter and the Rives tones and I only had to boost ever so slightly at a few points. However, I am only using the EQ below 80Hz. To fix the upper areas I had lower my woofer sections overall level. I have my receiver bi-amped so I just lowered them a few db's this also helped out from 600 to 2500 as well because it was a little high there too.

If you are not bi-amping your receiver, this is a good reason to do so, providing both your speakers and receiver are capable. If not then you will have to find the best compromise.

The Rives CD does not have tones in between those on the graph below so I am not sure what the response is in between those frequencies. I would like to see just how flat is in smaller steps 30,35,40,45 Hz etc. That is my second complaint. Rives doesn't mention it so maybe I am worrying for nothing but it would be a comfort for people like me to know. I also found out that my room has some very strange things going on when have the sub facing forward. If I changed the position of the meter slightly I would get totally different readings and it was hard to tell just where it should be facing. I was able to correct this by down firing the sub. Once it was facing down this all but disappeared on the low frequencies. Again, without these tones I would have never of known this. So thank you Rives!

After going through the rest of the tones out to 20Khz I found out my room wasn't to bad, aside from the expected few nulls and a peaks. Within the limits of this test, I found no peaks over 6db and only one null of -10db at 250Hz. All this is according to my SPL meter and the Rives tones. Since I have no other equipment to verify my results with, I can only go with what I have. I am sure it is not perfect but I am also sure it is closer than it was before. If the end result is better sounding bass for less money, than I have achieved the goal this CD was intended for. Rives mentions not to worry too much about the nulls and I have read several other sources that say the same thing. Not much you can do about them anyway until you get serious about treating the room, and that is something that I will do when my wife and I buy a new home.

Listening to the Results

Once I was satisfied with my results, I grabbed my favorite music and sat down and listen to the fruits of my labor. I was not disappointed. The first song I played was of the DVD audio version of "What's New" by Linda Ronstadt. This entire disk never sounded correct in the past. It always sounded boomy and too heavy in the bass. Now it was completely changed. It was very smooth and laid back, but not lacking or weak and it still reached with authority into the lower octaves. I could now clearly and distinctly hear the separate notes on the bass, where before they were completely obscured. The vocals seemed to come alive, her voice now sounded like she was in the same room and standing right in front of me. Something that I now know was being covered over by that severe peak at 63Hz that I had. Next I put on the DVD Audio version of " The Night Fly" by Donald Fagen. It did not matter which track I played, they all sounded natural, the boomy sound completely gone, vocals and mid-bass cleared right up. Lastly, was Diana Krall's DVD "Live in Paris " in DTS. Before, the bass on this disk overwhelmed everything so much that I had to back it down when I played it. Now the bass seemed natural and balanced and I could clearly hear every note change and nuance on the stand up bass. I am very happy with the bass in my room now, next up is a sub that can go lower.

Conclusions

After spending several hours with this test CD, I can definitely recommend it for someone who has an EQ and would like to attempt to improve their bass response If you don't have an EQ then it can help you find the location where your sub has the flattest response. For only $18 plus shipping this is one of the least expensive investments you can make to your system.

I would like to know if there is a more accurate SPL meter that Rives would recommend. I have seen several different ones on the net and I am wondering if even better results could be achieved. Also, which set of tones would one use for Radio Shacks new digital Meter?

So armed with your trusty Radio Shack SPL meter an EQ and the Rives Audio Test CD 2, you now have an inexpensive and more accurate way to meld your sub into the rest of your system. The CD can be ordered directly from Rives at www.rivesaudio.com . This CD now proudly sits on the shelf right next to my AVIA and Digital Video Essentials disks and I think that is pretty good company indeed.

Reference Equipment

  • Denon AVR-2803
  • Denon DVD-2200
  • ART 352 31 band graphic equalizer (Inline with the subwoofer only)
  • Paradigm PDR 10 (Subwoofer crossed over by the receiver at 80Hz)
  • Paradigm Monitor 7's (Set to small with the receiver)

 

About the author:

Clint Deboer was terminated from Audioholics for misconduct on April 4th, 2014. He no longer represents Audioholics in any fashion.

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